The present invention relates to optical communication module and the manufacturing method thereof.
In recent years, the larger volume of transmission is anxiously demanded for optical fiber communication. Thus, wavelength multiplexing optical communication system is put into practice to transmit a plurality of lights having different wavelength through the sole optical fiber so as to enlarge the volume of transmission. The wavelengths used for that purpose are restricted within the band of 1.3 xcexcm or 1.55 xcexcm, which means that the narrowing of an interval between the adjacent wavelengths leads to the increase of the number of wavelengths that can be transmitted. The wavelengths in use are standardized as an ITU grid by the recommendation of ITU (International Telecommunication Union), the frequency interval or spacing of which wavelengths tends to become narrower from 200 GHz via 100 GHz to 50 GHz, which correspond to 1.6 nm, 0.8 nm and 0.4 nm in terms of wavelength intervals. It requires a highly precise stabilization of the respective wavelengths to narrow the wavelength intervals, which leads to the demand for an optical communication module as a luminous source for stabilizing an oscillating wavelength of a semiconductor laser.
In respect of the optical communication module to stabilize the oscillating wavelength of the semiconductor laser, there are some prior methods for monitoring and stabilizing the wavelengths. Especially, an etalon filter (etalon) having repetitive wavelength selectivity is advantageous for detecting the plurality of different wavelengths by means of the sole etalon, which use is prevailing. There is a disclosure relevant to the method for detecting and stabilizing wavelengths in Japanese Patent Application Laid-open No. Hei 10-079723 entitled xe2x80x9cWavelength Monitoring and Controlling Apparatus for Wavelength Segmenting Multiplex Optical Transmission Systemxe2x80x9d, in which the laser beam diffused by a lens is diagonally emitted to an etalon, and the difference in transmitted quantity of light between two separate places respectively having different incident angle is detected by a photodiode.
As for an example of the method for rendering the laser beam parallel light and divide the same light into two parts by means of a beam splitter, one of which parts is practically vertically emitted with regard to an etalon, so as to detect and stabilize wavelengths, there is a prior disclosure described in the presentation entitled xe2x80x9cWavelength Detecting Section Integrated Tunable LD Modulexe2x80x9d at the General Convention C-3-143 of Electronics, Information and Communication Academy in May 2000. Then, in the Japanese Patent Application Laid-open No.2000-223747 entitled xe2x80x9cLight Emitting Devicexe2x80x9d, it is disclosed that only a portion of the laser beam is emitted to an etalon without using the beam splitter.
Further, in the Japanese Patent Application Laid-open No. Hei 10-079723 as described above, it is disclosed that the etalon swings to the horizontal direction with regard to the substrate.
It is for sure that the utilization of the repetitive wavelength selectivity of the etalon allows the sole etalon to detect the plurality of different wavelengths, but it requires a highly precise adjustment and fixing of the incident angle of the beam with regard to the etalon to detect the change in the vicinity of a particular wavelength.
As an example of the method for adjusting the incident angle of the laser with regard to the etalon, the method for swinging the laser beam to the horizontal direction with regard to the substrate is disclosed in the Japanese Patent Application Laid-open No. Hei 10-079723, but it is insufficient to prevent the transmitted quantity of light of the laser from decreasing in light of the characteristics of the etalon, in the event where the incident angle of the laser with regard to the laser becomes larger.
Thus, for any of the foregoing prior disclosures, it requires to highly precisely adjust and fix the incident angle of the etalon by swinging the etalon in the vicinity of the vertical incident angle thereof.
The present invention is to provide a technical solution to finely tune the incident angle of the laser with regard to the etalon.
The present invention is also to provide optical communication module capable of highly precisely adjusting the incident angle of the laser with regard to the etalon for the detection of the plurality of different wavelengths by means of the repetitive selectivity of the etalon.
The first embodiment of the present invention relates to optical communication module comprising a semiconductor laser, a lens converting the beam emitted from the laser, a wavelength selective filter for the laser beam as converted and a light receiving device of the beam transmitted through the filter, wherein the filter is cylindrical in shape and provided with a plane of incidence and a plane of emission substantially parallel to each other, the slope of which plane of incidence has an angle excepting 0 degree with regard to the central axis of the cylinder.
The use of such cylindrical filter as above that revolves around the central axis thereof allows the transmitted quantity of light of the etalon to be adjusted, which facilitates the transmitted quantity of light of the etalon with respect to a particular wavelength to be set at a target value.
The second embodiment hereof relates to optical communication module comprising a semiconductor laser, a lens converting the beam emitted from the laser, a wavelength selective filter of the beam as converted and a light receiving device of the beam transmitted through the filter, wherein the filter is provided with a plane of incidence and a plane of emission substantially parallel to each other and at least one lateral plane between those two planes, which filter is fixed onto the substrate so that there is an angle above 0 degree between the lateral plane and the substrate.
The present invention allows the filter to be positioned at the lateral plane at one time and to be further rotated, which facilitates the transmitted quantity of light of the etalon to be adjusted.
Further, providing that a holding member to hold an angle is provided for stabilization between the lateral plane of the filter and the substrate, it prevents the augmented transmitted quantity of light of the etalon from fluctuating.
The filter may be fixed on the substrate by soldering, but the metallization of the lateral plane surface improves the adhesion between the solder and the filter.
Further, the formation of the plurality of the lateral planes allows the filter to be fixed at any one of such planes, which enables the transmission characteristics of the filter to be stepwise controlled.
Moreover, the adjoining disposition of the lateral planes allows the transmission characteristics of the filter to change in a continuous and stepwise manner.
Also, the markings on the filter allow the transmission characteristics of the etalon in each direction of the filter to be grasped, which markings turn to become reference points to change the transmission characteristics thereof through the revolution of the filter so as to facilitate the fixing of the same on the substrate.
In turn, upon the disposition of the filter on the substrate, the markings on the substrate to position the filter thereon allow the counterpart markings or uneven surface of the filter to go aligned to each other, which also facilitates the filter to be fixed on the substrate.
Providing that a filter is produced such that it is disposed on the optical communication module by displacing by a first angle the slope of the plane of incidence of the filter with regard to the optical axis of the beam and rotating the filter around an axis with a second angle different from the first angle, it facilitates the characteristics of the filter to change upon its disposition on the substrate.
Further, provided that the filter is rotated around the central axis of the beam emitted from the semiconductor laser or parallelwise to the central axis, it allows more preferred transmission characteristics of the filter to be selected.
Then, provided that the center of a lens is offset vertically with regard to the central axis of the beam, it allows more preferred transmission characteristics of the filter to be obtained.
Differently from the embodiments as described above, another embodiment relates to an optical communication module comprising a semiconductor laser, a lens converting the beam emitted from the laser, a wavelength selective filter of the beam as converted and a light receiving device of the beam transmitted through the filter, wherein the plane of emission of the lens is inclined from the vertical direction with regard to the rotational axis of the filter.
This embodiment allows the transmission characteristics of the filter to easily change, which facilitates the transmitted quantity of light of the etalon to be set at a target value.
Further, a portion of the beam as converted is through the wavelength selective filter received into a light receiving device while the remaining portion thereof is received into another light receiving device so as to perform monitoring on wavelengths, which allows the disposition of the respective structural members to be controlled so as to adjust the transmitted quantity of light of the filter.
Further, differently from the embodiments as mentioned above, another embodiment relates to an optical communication module comprising a semiconductor laser, a lens converting the beam emitted from the laser, a wedge substrate converting the direction of the beam as converted, a wavelength selective filter of the beam as converted and a light receiving device receiving the beam transmitted through the filter, wherein the plane of emission of the wedge substrate is inclined from the vertical direction with regard to the rotational axis of the filter, which substrate rotates around the optical axis of the beam.
This embodiment also facilitates the transmitted quantity of light of the filter to be easily adjusted.
To note, it is preferred to use a wedge substrate, on the plane of incidence of which substrate a semi-transparent film is attached.
When a wavelength selective filter that transmits a portion of light wavelengths, which filter is provided with a plane inclined with regard to the central axis of a cylinder and a metallized portion along the circumferential portion of the cylinder that allows for spot welding by laser beam, is adopted for the filter of the optical communication module, it facilitates the transmission characteristics of the filter to be easily adjusted.
When a method for producing a wavelength selective filter provided with a plane inclined with regard to the central axis of the cylinder and transmitting a portion of light wavelengths, along the outer circumference of which cylinder a metallized portion for soldering is provided, is put to practical use, it facilitates the transmission characteristics of the filter to be easily adjusted.
Those and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.